Artificial and supplemental lighting in e.g. a greenhouse typically involves use of an illumination system for stimulating plant growth, the illumination system comprising a plurality of high power light sources. Different types of light sources, having different light spectrums and providing different effects on growth stimulation, may be included, such as light sources based on metal halide (MH) or high intensity discharge (HID) which includes high pressure sodium (HPS). Using metal halide based lighting typically promotes shorter, bushy growth; whereas high pressure sodium based lighting in comparison typically tend to produce taller and stretched plants.
Recently, much progress has been made in increasing the brightness of light emitting diodes (LEDs). As a result, LEDs have become sufficiently bright and inexpensive to serve also for artificial lighting in e.g. a greenhouse environment, additionally providing the possibility of emitting light with adjustable color (light spectrum). By mixing differently colored LEDs any number of colors can be generated. An adjustable color lighting system typically comprises a number of primary colors, for one example the three primaries red, green and blue. The color of the generated light is determined by the LEDs that are used, as well as by the mixing ratios. By using LEDs it is possible to decrease the energy consumption, a requirement that is well in line with the current environmental trend. Additionally, using LED based illumination system minimizes the amount of light source generated heat which is specifically suitable in an environment where temperature control is desirable.
An example of an LED based illumination system is disclosed in WO2008118080, comprising a light sensor communicatively coupled to a processor, where the processor implements a control algorithm for modulating and improving plant growth and attributes by adjusting the light emitted by the LEDs.
WO2008118080 shows a promising approach in relation to artificial lighting in a greenhouse environment, however, it would still be desirable to further optimize the artificial and/or supplemental light emitted by an illumination system, to be able to improve the growth process of a plant.